1. Technical Field
The present invention relates to a yellow ink composition that yields recorded matter with excellent print quality and that is also highly resistant to light and has excellent ozonefastness, and that allows hue adjustment and ozonefastness adjustment, has stable discharge reliability, and is favorable for inkjet recording, and to an ink set and an ink cartridge in which this composition is used, and to an inkjet recording method and recorded matter in which these are used.
2. Related Art
Inkjet recording is a known method in which droplets of an ink composition are discharged from a fine nozzle and adhere to the surface of a recording medium to record text or graphics. Inkjet recording methods that have seen practical application include (i) a method in which an electrostrictive element is used to convert an electrical signal into a mechanical signal, an ink composition stored in a nozzle head is intermittently discharged from the nozzle head according to this mechanical signal, and the ink composition adheres to a recording medium surface to record text or graphics, and (ii) a method in which the portion of the nozzle head that is extremely close to the discharge component is rapidly heated, bubbles are generated in an ink composition stored in the nozzle head portion, the volumetric expansion of the bubbles causes the ink composition to be intermittently discharged from the nozzle head, and the ink composition adheres to a recording medium surface to record text or graphics.
Today, a plurality of color ink compositions are readied and a color image is formed by inkjet recording. In general, a color image is formed by the three colors a yellow ink composition, a magenta ink composition, and a cyan ink composition, and in some cases by four colors additionally including a black ink composition. There are also cases in which a color image is formed by six colors (by adding a light cyan ink composition and a light magenta ink composition to the above four colors), or even seven colors (by further adding a dark yellow ink composition). An ink set is the product of thus combining two or more types of ink composition, and is usually used by being mounted in a printer in the form of an ink cartridge that accommodates this ink set.
The ink compositions used in inkjet recording are generally solutions obtained by dissolving various dyes in water, an organic solvent, or a mixture of these, and an ink composition used to form such a color image needs to have good color expression itself, and also needs to express good intermediate colors when a plurality of ink compositions are combined, not to fade in color over time when printed matter is stored, and so forth.
Also, through continuous improvement to heads, ink compositions, recording methods, and media, the printing of photographic images with a color inkjet printer has in recent years reached a level that is comparable to that of silver halide photographs, and image quality is now as good as that of photographs. Meanwhile, improvements to ink compositions and media have resulted in better storage stability of the resulting images. Lightfastness in particular has been improved to a level that no longer poses any practical problems.
Nevertheless, the quality has yet to equal that of silver halide photographs. The standard way to evaluate lightfastness performance is to use as an index the fading of patterns of pure color of yellow, magenta, and cyan (whose optical density is close to 1.0). When the lightfastness performance of ink compositions used in current printers that are available on the market is evaluated by the above method, a magenta ink composition has the lowest performance, and it is often the case that the lightfastness of an ink set is the determining factor in its service life.
Improving the lightfastness of a magenta ink composition is effective at extending the lightfastness service life of an ink set and increasing the lightfastness of a photographic image, so a great deal of developmental improvement has gone into new magenta ink compositions with excellent lightfastness service lives, and many proposals have been made (see JP-A-2005-105136 and JP-A-2002-371079, for example).
Accordingly, as the performance (lightfastness characteristics) of magenta inks has increased through these improvements to magenta inks, it has become essential to improve the characteristics of colorants of other colors used in ink sets, and particularly those of yellow inks.
Numerous improvements have been made in the past to yellow inks in which yellow colorants are used (see JP-A-2000-154344, JP-A-2000-345080, and JP-A-2005-320530, among others), and many of these have been put to practical use, but compared to magenta ink compositions that have undergone various improvements and seen practical application in recent years, conventional yellow inks (yellow ink compositions) have lower lightfastness and ozonefastness, and have poor variation in their yellow hues, and this makes it difficult to adjust their hue, among other drawbacks, and improvement is needed in this area.